We have studied the effect of Ga substitution on the magnetic and tran
sport properties of MnPtAl1-xGax compounds with x = 0, 0.05, 0.1, 0.15
and 0.2. With increasing Ga concentration, we find a rather weak line
ar reduction of the Neel temperature. However, the metamagnetic field
associated with the field-induced ferromagnetic alignment is strongly
reduced. The results are discussed in the framework of competing Mn-Mn
interactions. (C) 1998 Elsevier Science B.V. All rights reserved.